Ring-opening polymerization refers to a process whereby cycloolefins, in the presence of an olefin metathesis catalyst, form high molecular weight polyalkenamers. ##STR2## It should be noted that in polyalkenamers resulting from the ring-opening polymerization of cycloolefins, the repeating polymer segments contain essentially the same number of carbon atoms and double bonds as the cyloolefin polymerized. This is to be contrasted with addition polymers prepared from acyclic olefins and diolefins, wherein the polymer segments contain one less double bond than the employed olefin or diolefin monomer contained.
The present invention is specific for ring-opening copolymerizations of Hex COD (I) and a cycloolefin comonomer as defined above. Representative of such cycloolefins are cyclopentene, cyclooctene and 1,5-cyclooctadiene. Owing to the possession of chlorine atoms, copolymers prepared with Hex COD (I) possess oil-, chemical-, and flame-resistant properties which are useful in numerous applications and are described in an earlier patent, U.S. Pat. No. 3,634,374, granted Jan. 11, 1972.
Copolymerization of Hex COD (I) can be initiated by conventional tungsten-based olefin metathesis catalyst systems, as set forth in U.S. Pat. Nos. 3,597,403 granted Aug. 3, 1971; 3,634,374 granted Jan. 11, 1972; 3,722,255 granted Nov. 13, 1973; 3,867,361 granted Feb. 18, 1975; 3,932,373 granted Jan. 13, 1976; and 3,943,116 granted Mar. 9, 1976. However, with the use of such prior art catalysts, the copolymerizations are marked by the phenomenon that by comparison with the charged comonomer ratio, only a very small level of the chlorine-containing Hex COD comonomer is incorporated into the copolymer during the initial and early stages of the polymerization, owing to its relatively lower reactivity. Hence, it is only when the concentration of the cycloolefin comonomer is substantially diminished during the polymerization that the chlorine content of the copolymer gradually approaches the theoretical level based on the initial comonomer charge. One of the primary disadvantages of this feaure is that the chlorine-content desired for a particular copolymer is not achieved when less than quantitative (100 percent) yields of the copolymer are obtained.